(Benzo­furan-2-yl)(3-methyl-3-phenyl­cyclo­butyl)­methanone

The structure of the title compound, C₂₀H₁₈O₂, consists of a dimeric arrangement of benzo­furan mol­ecules around an inversion centre, linked via C—H...O hydrogen bonds. There are also C—H...π ring interactions. All these interactions result in the formation of infinite chains parallel to the [100] axis. The cyclo­butane ring is puckered, with a dihedral angle of 29.03 (13)° between the two three-atom planes.

S1. Comment

Benzofurans have attracted widespread interest, in view of their biological activity, their presence in a large number of natural products and their potential as pharmacological agents. Consequently, diverse synthetic strategies have been developed to build this fused skeleton, commonly starting from a benzene ring with the appropriate substituents. A large number of syntheses of the heterocyclic moiety in benzofuran are based on the formation of O1—C5 or C5—C6 bonds as the ring-closure step (Cruz & Tamariz, 2004). In this paper, we report the molecular and crystal structure of the title benzofuran, (I). \sch

The present crystal structure determination of (I) was carried out to determine the strength of the hydrogen-bonding capabilities of benzofuran and carbonyl, as well as of the C—H···π interactions between the molecules. Compound (I) consists of cyclobutyl and benzofuran rings linked through a carbonyl group (Fig. 1). Selected bond lengths and angles in (I) are shown in Table 1.

The dihedral angles between the phenyl ring A (C15—C20), the cyclobutane ring B (C1—C4), the benzofuran ring C (O1/C5/C6/C7/C12) and the benzene ring D (C7—C12) are A/B 32.74 (10), A/C 73.60 (6), A/D 73.66 (6), B/C 46.34 (10), B/D 45.81 (9) and C/D 1.64 (14)°, i.e. rings C and D are nearly coplanar. The steric interaction between the substituent groups on the cyclobutane ring means that this ring deviates significantly from planarity. Literature values for the puckering of the cyclobutane ring are 23.5° (Swenson et al., 1997) and 2.89 (37)° (Özdemir et al., 2004a). In this study, the C4/C1/C2 plane forms a dihedral angle of 29.03 (13)° with the C2/C3/C4 plane, which deviates from the values reported in the previous studies. The geometry of the cyclobutane ring is due to the steric effect of the methyl group. The C2—C1—C13—C5 torsion angle is −177.46 (16)°.

In this compound, atom H16 of the A ring (C15—C20) acts as a donor, resulting in the formation of C—H···O hydrogen bonds which link two molecules related by an inversion centre (Fig. 2). Of greater interest are the intermolecular π-ring interactions between the H atoms of the cyclobutane and the benzofuran rings, which contribute to the crystal packing by forming an infinite chain of dimers. These C—H···π interactions, between rings D and C, the benzofuran rings, and atoms H1(C1) and H2B(C2) of the cyclobutane, have the following geometric parameters. Firstly, the distance between atom H1 bonded to atom C1 and the centre, M, of ring Dⁱⁱ (C7—C12) is 2.716 Å [symmetry code: (ii) x − 1, y, z] and the C1—H1···M angle is 135.1°. Secondly, the distance between atom H2B bonded to atom C2 and the centre, K, of ring Cⁱⁱ (C5/C6/C7/C12/O1), is 2.779 Å and the C2—H2B···K angle is 142.0°.

The results obtained in this study indicate that there are some differences in the geometry of (I) compared with that of other compounds containing benzofuran or cyclobutane groups, such as those reported by Batsanov & Perepichka (2002) and Özdemir et al. (2004 Which reference?). In the reported study (Which?), the crystal packing is mainly stabilized by intermolecular hydrogen bonds, which are highly effective in forming polymeric chains (Özdemir et al., 2004b). From the results presented in this paper, it can be said that C—H···O hydrogen bonds link two molecules through an inversion centre to form a dimer, similar to what was found by Batsanov & Perepichka (2002). Besides these hydrogen bonds, there is an interesting π-ring interaction which stabilizes the crystal structure of (I). Dipole-dipole and van der Waals interactions are also effective in the molecular packing in the crystal structure.

S2. Experimental

Salicylaldehyde (1.342 g, 1.15 ml, 11 mmol), potassium carbonate (2.07 g, 15 mmol) and acetonitrile (100 ml) were placed in a 500 ml two-necked flask fitted with a reflux condenser, and the mixture was stirred for 1 h at room temperature. To this solution, a solution of 1-phenyl-1-methyl-3-(2-chloro-1-oxoethyl)cyclobutane (2.225 g, 10 mmol) in acetonitrile (100 ml) was added dropwise over a period of about 30 min. and refluxed for 4 h. The course of the reaction was monitored by IR spectroscopy. The solvent was removed under reduced pressure, the residue was extracted with diethyl ether and the ether phase was dried on magnesium sulfate. After filtration and removal of the solvent under reduced pressure, compound (I) was crystallized from acetonitrile (yield 84%, m.p. 429–430 K).

S3. Refinement

H atoms were placed in idealized positions, with C—H distances in the range 0.93–0.98 Å and U_iso(H) = 1.2U_eq(C) (1.5 for the methyl group).

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. A drawing of the molecule of (I), with the atom-numbering scheme. Displacement ellispoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A diagram showing the hydrogen-bonding and π-ring interactions in (I). Displacement ellipsoids are drawn at the 30% probability level. [Symmetry codes:(i) 1 − x, 1 − y, 1 − z; (ii) x − 1, y, z].

(Benzofuran-2-yl)(3-methyl-3-phenylcyclobutyl)methanone

Crystal data

C20H18O2	F(000) = 616
Mr = 290.34	Dx = 1.263 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 5297 reflections
a = 6.1497 (7) Å	θ = 1.8–26.8°
b = 14.6894 (19) Å	µ = 0.08 mm^−1
c = 16.922 (2) Å	T = 293 K
β = 92.60 (1)°	Rod, colourless
V = 1527.1 (3) Å^3	0.50 × 0.25 × 0.11 mm
Z = 4

Data collection

Stoe IPDS 2 diffractometer	1602 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.117
Graphite monochromator	θmax = 25.0°, θmin = 1.8°
Detector resolution: 6.67 pixels mm^-1	h = −7→7
ϕ scans	k = −17→17
11652 measured reflections	l = −20→20
2685 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.041	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.098	H-atom parameters constrained
S = 0.83	w = 1/[σ^2(Fo^2) + (0.0453P)^2] where P = (Fo^2 + 2Fc^2)/3
2685 reflections	(Δ/σ)max < 0.001
200 parameters	Δρmax = 0.13 e Å^−3
0 restraints	Δρmin = −0.16 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	1.14325 (19)	0.24820 (8)	0.50310 (7)	0.0453 (3)
O2	0.8586 (2)	0.44383 (10)	0.56316 (8)	0.0604 (4)
C1	0.7713 (3)	0.34439 (12)	0.45466 (11)	0.0411 (4)
H1	0.7294	0.2807	0.4621	0.049*
C2	0.5732 (3)	0.39917 (14)	0.42493 (11)	0.0455 (5)
H2A	0.5822	0.4635	0.4375	0.055*
H2B	0.4354	0.3737	0.4399	0.055*
C3	0.6323 (3)	0.37619 (12)	0.33906 (10)	0.0389 (4)
C4	0.8655 (3)	0.35623 (13)	0.37205 (10)	0.0429 (5)
H4A	0.9645	0.4073	0.3684	0.051*
H4B	0.9283	0.3011	0.3512	0.051*
C5	1.0984 (3)	0.32396 (12)	0.54943 (10)	0.0402 (5)
C6	1.2504 (3)	0.33428 (12)	0.60813 (11)	0.0447 (5)
H6	1.2542	0.3798	0.6464	0.054*
C7	1.4058 (3)	0.26243 (13)	0.60122 (11)	0.0429 (5)
C8	1.6002 (3)	0.23670 (14)	0.64054 (12)	0.0534 (5)
H8	1.6544	0.2692	0.6843	0.064*
C9	1.7101 (3)	0.16238 (14)	0.61349 (13)	0.0565 (6)
H9	1.8398	0.1444	0.6394	0.068*
C10	1.6306 (3)	0.11371 (14)	0.54820 (13)	0.0557 (6)
H10	1.7087	0.0637	0.5312	0.067*
C11	1.4401 (3)	0.13709 (13)	0.50778 (13)	0.0514 (5)
H11	1.3866	0.1042	0.4641	0.062*
C12	1.3323 (3)	0.21215 (12)	0.53570 (11)	0.0409 (5)
C13	0.9046 (3)	0.37640 (13)	0.52525 (11)	0.0431 (5)
C14	0.5176 (4)	0.28878 (13)	0.31006 (14)	0.0608 (6)
H14A	0.3645	0.3002	0.3019	0.091*
H14B	0.5400	0.2417	0.3490	0.091*
H14C	0.5765	0.2697	0.2612	0.091*
C15	0.5987 (3)	0.44929 (12)	0.27737 (10)	0.0396 (4)
C16	0.4100 (3)	0.50051 (13)	0.27306 (12)	0.0493 (5)
H16	0.3054	0.4917	0.3103	0.059*
C17	0.3746 (4)	0.56472 (14)	0.21401 (14)	0.0612 (6)
H17	0.2463	0.5983	0.2117	0.073*
C18	0.5278 (5)	0.57890 (15)	0.15901 (15)	0.0707 (7)
H18	0.5044	0.6221	0.1193	0.085*
C19	0.7172 (4)	0.52849 (18)	0.16311 (13)	0.0724 (7)
H19	0.8223	0.5380	0.1262	0.087*
C20	0.7517 (3)	0.46405 (15)	0.22153 (12)	0.0567 (5)
H20	0.8795	0.4301	0.2233	0.068*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0512 (8)	0.0414 (7)	0.0429 (7)	−0.0010 (6)	−0.0042 (6)	−0.0052 (6)
O2	0.0709 (10)	0.0553 (9)	0.0549 (9)	0.0100 (7)	0.0028 (8)	−0.0135 (7)
C1	0.0445 (10)	0.0386 (10)	0.0403 (10)	−0.0022 (8)	0.0034 (9)	0.0022 (8)
C2	0.0443 (11)	0.0518 (12)	0.0410 (11)	0.0014 (9)	0.0068 (9)	0.0056 (9)
C3	0.0438 (10)	0.0375 (9)	0.0355 (10)	−0.0017 (8)	0.0020 (9)	−0.0003 (8)
C4	0.0472 (10)	0.0419 (10)	0.0400 (11)	0.0026 (9)	0.0055 (9)	−0.0022 (8)
C5	0.0480 (11)	0.0362 (10)	0.0366 (10)	−0.0020 (9)	0.0036 (9)	−0.0036 (8)
C6	0.0568 (12)	0.0399 (10)	0.0371 (11)	−0.0024 (9)	−0.0016 (9)	−0.0024 (8)
C7	0.0502 (11)	0.0395 (10)	0.0387 (10)	−0.0055 (9)	−0.0007 (9)	0.0037 (8)
C8	0.0627 (13)	0.0497 (12)	0.0468 (12)	−0.0042 (11)	−0.0089 (11)	0.0023 (10)
C9	0.0587 (12)	0.0519 (12)	0.0579 (14)	0.0052 (11)	−0.0076 (11)	0.0119 (11)
C10	0.0661 (14)	0.0402 (11)	0.0609 (14)	0.0067 (10)	0.0019 (12)	0.0046 (10)
C11	0.0618 (13)	0.0406 (11)	0.0514 (12)	−0.0009 (10)	−0.0031 (11)	−0.0025 (9)
C12	0.0462 (11)	0.0352 (10)	0.0408 (11)	−0.0049 (8)	−0.0023 (9)	0.0016 (8)
C13	0.0515 (11)	0.0406 (10)	0.0379 (10)	−0.0040 (9)	0.0082 (9)	0.0030 (9)
C14	0.0726 (14)	0.0442 (12)	0.0640 (14)	−0.0102 (10)	−0.0148 (12)	0.0035 (10)
C15	0.0460 (11)	0.0383 (10)	0.0346 (10)	−0.0026 (8)	0.0004 (9)	−0.0028 (8)
C16	0.0527 (11)	0.0474 (11)	0.0475 (12)	0.0030 (10)	−0.0004 (10)	−0.0023 (9)
C17	0.0733 (15)	0.0458 (12)	0.0627 (15)	0.0086 (11)	−0.0172 (13)	−0.0032 (11)
C18	0.0996 (19)	0.0518 (13)	0.0593 (15)	−0.0098 (14)	−0.0133 (15)	0.0162 (12)
C19	0.0839 (17)	0.0785 (17)	0.0560 (14)	−0.0071 (15)	0.0161 (13)	0.0220 (13)
C20	0.0611 (13)	0.0592 (13)	0.0507 (12)	0.0050 (11)	0.0109 (11)	0.0086 (10)

Geometric parameters (Å, º)

O1—C12	1.371 (2)	C8—H8	0.9300
O1—C5	1.396 (2)	C9—C10	1.386 (3)
O2—C13	1.220 (2)	C9—H9	0.9300
C1—C13	1.494 (2)	C10—C11	1.374 (3)
C1—C2	1.526 (2)	C10—H10	0.9300
C1—C4	1.547 (3)	C11—C12	1.381 (3)
C1—H1	0.9800	C11—H11	0.9300
C2—C3	1.551 (3)	C14—H14A	0.9600
C2—H2A	0.9700	C14—H14B	0.9600
C2—H2B	0.9700	C14—H14C	0.9600
C3—C15	1.505 (2)	C15—C20	1.380 (3)
C3—C14	1.535 (2)	C15—C16	1.382 (3)
C3—C4	1.543 (2)	C16—C17	1.384 (3)
C4—H4A	0.9700	C16—H16	0.9300
C4—H4B	0.9700	C17—C18	1.370 (3)
C5—C6	1.341 (2)	C17—H17	0.9300
C5—C13	1.462 (3)	C18—C19	1.379 (3)
C6—C7	1.432 (3)	C18—H18	0.9300
C6—H6	0.9300	C19—C20	1.378 (3)
C7—C12	1.390 (3)	C19—H19	0.9300
C7—C8	1.394 (2)	C20—H20	0.9300
C8—C9	1.374 (3)
C12—O1—C5	105.52 (13)	C8—C9—H9	119.5
C13—C1—C2	119.90 (16)	C10—C9—H9	119.5
C13—C1—C4	118.23 (15)	C11—C10—C9	122.0 (2)
C2—C1—C4	88.21 (13)	C11—C10—H10	119.0
C13—C1—H1	109.6	C9—C10—H10	119.0
C2—C1—H1	109.6	C10—C11—C12	116.17 (19)
C4—C1—H1	109.6	C10—C11—H11	121.9
C1—C2—C3	88.67 (14)	C12—C11—H11	121.9
C1—C2—H2A	113.9	O1—C12—C11	125.61 (16)
C3—C2—H2A	113.9	O1—C12—C7	110.77 (16)
C1—C2—H2B	113.9	C11—C12—C7	123.62 (17)
C3—C2—H2B	113.9	O2—C13—C5	119.06 (16)
H2A—C2—H2B	111.1	O2—C13—C1	122.99 (17)
C15—C3—C14	109.18 (14)	C5—C13—C1	117.95 (16)
C15—C3—C4	118.83 (16)	C3—C14—H14A	109.5
C14—C3—C4	111.27 (15)	C3—C14—H14B	109.5
C15—C3—C2	117.64 (15)	H14A—C14—H14B	109.5
C14—C3—C2	110.97 (16)	C3—C14—H14C	109.5
C4—C3—C2	87.45 (13)	H14A—C14—H14C	109.5
C3—C4—C1	88.19 (13)	H14B—C14—H14C	109.5
C3—C4—H4A	114.0	C20—C15—C16	118.35 (18)
C1—C4—H4A	114.0	C20—C15—C3	120.71 (17)
C3—C4—H4B	114.0	C16—C15—C3	120.88 (18)
C1—C4—H4B	114.0	C15—C16—C17	120.9 (2)
H4A—C4—H4B	111.2	C15—C16—H16	119.6
C6—C5—O1	110.92 (15)	C17—C16—H16	119.6
C6—C5—C13	132.83 (17)	C18—C17—C16	120.2 (2)
O1—C5—C13	116.25 (14)	C18—C17—H17	119.9
C5—C6—C7	107.55 (16)	C16—C17—H17	119.9
C5—C6—H6	126.2	C17—C18—C19	119.3 (2)
C7—C6—H6	126.2	C17—C18—H18	120.4
C12—C7—C8	118.50 (18)	C19—C18—H18	120.4
C12—C7—C6	105.24 (15)	C20—C19—C18	120.5 (2)
C8—C7—C6	136.21 (18)	C20—C19—H19	119.8
C9—C8—C7	118.76 (18)	C18—C19—H19	119.8
C9—C8—H8	120.6	C19—C20—C15	120.8 (2)
C7—C8—H8	120.6	C19—C20—H20	119.6
C8—C9—C10	120.94 (19)	C15—C20—H20	119.6
C13—C1—C2—C3	142.35 (17)	C6—C7—C12—O1	−0.4 (2)
C4—C1—C2—C3	20.48 (13)	C8—C7—C12—C11	0.8 (3)
C1—C2—C3—C15	−141.99 (16)	C6—C7—C12—C11	178.70 (18)
C1—C2—C3—C14	91.29 (16)	C6—C5—C13—O2	−0.7 (3)
C1—C2—C3—C4	−20.54 (13)	O1—C5—C13—O2	−179.31 (17)
C15—C3—C4—C1	140.63 (16)	C6—C5—C13—C1	179.4 (2)
C14—C3—C4—C1	−91.28 (18)	O1—C5—C13—C1	0.7 (2)
C2—C3—C4—C1	20.26 (13)	C2—C1—C13—O2	2.7 (3)
C13—C1—C4—C3	−143.91 (16)	C4—C1—C13—O2	108.2 (2)
C2—C1—C4—C3	−20.59 (13)	C2—C1—C13—C5	−177.30 (17)
C12—O1—C5—C6	−0.42 (19)	C4—C1—C13—C5	−71.8 (2)
C12—O1—C5—C13	178.52 (15)	C14—C3—C15—C20	−94.4 (2)
O1—C5—C6—C7	0.2 (2)	C4—C3—C15—C20	34.7 (2)
C13—C5—C6—C7	−178.55 (19)	C2—C3—C15—C20	138.01 (18)
C5—C6—C7—C12	0.2 (2)	C14—C3—C15—C16	82.7 (2)
C5—C6—C7—C8	177.4 (2)	C4—C3—C15—C16	−148.23 (17)
C12—C7—C8—C9	−0.6 (3)	C2—C3—C15—C16	−44.9 (2)
C6—C7—C8—C9	−177.6 (2)	C20—C15—C16—C17	0.3 (3)
C7—C8—C9—C10	0.2 (3)	C3—C15—C16—C17	−176.87 (16)
C8—C9—C10—C11	0.0 (3)	C15—C16—C17—C18	−0.5 (3)
C9—C10—C11—C12	0.3 (3)	C16—C17—C18—C19	0.1 (3)
C5—O1—C12—C11	−178.59 (19)	C17—C18—C19—C20	0.4 (4)
C5—O1—C12—C7	0.5 (2)	C18—C19—C20—C15	−0.6 (3)
C10—C11—C12—O1	178.34 (18)	C16—C15—C20—C19	0.2 (3)
C10—C11—C12—C7	−0.7 (3)	C3—C15—C20—C19	177.40 (19)
C8—C7—C12—O1	−178.29 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C16—H16···O2^i	0.93	2.59	3.390 (2)	145

Symmetry code: (i) −x+1, −y+1, −z+1.